Limits Continuity And Differentiability

Let \(f: R^{+} \longrightarrow R^{+}\) be a function satisfying \(f(x)-x=\lambda\) (constant), \(\forall x \in R^{+}\) and \(f(x f(y))=f(x y)+x, \forall x, y, \in R^{+}\). Then, \(\lim _\limits{x \rightarrow 0} \frac{(f(x))^{1 / 3}-1}{(f(x))^{1 / 2}-1}=\)